This invention relates generally to an air conditioning control system and more specifically to an air conditioning control system which includes a main control unit for maintaining a room at a relatively high temperature during the day and a secondary control unit for maintaining the room at a relatively low temperature during the night.
The desirability of maintaining a heated room at a relatively low temperature during the night in order to save energy is well recognized. In a similar way, it is common practice to maintain a cooled room at a higher temperature at night or during periods of non-occupancy to save energy. Some known devices for maintaining a room at a relatively low temperature at night include electric clocks which are used in association with thermostatic controls to effect a reduction in the temperature of the room at night. One of the problems encountered with utilizing these known timers is that the clocks usually operate on line voltage while the thermostatic controls operate on a lower voltage. This requires separate wiring for the clock and thermostatic controls. If it is desired to fit an existing thermostatic control with a clock in order to provide for reduced temperatures at night, it is necessary to run power lines through existing walls of a building to supply electrical energy to the clock or to run the power line on the outside of the wall in an unsightly manner. Therefore, these known clock-type thermostatic controls which require two different voltages, that is a high voltage to operate the clock and a low voltage to operate the thermostatic controls, have been difficult to install in existing buildings. Some of these known controls which include clocks are illustrated in U.S. Pat. Nos. 2,558,617; 2,384,373; 2,375,234; and 1,316,517.
The problem of providing a relatively high voltage to operate an electrical clock associated with a thermostat is eliminated by utilizing a manually wound clock. However, if the manually wound clock is associated with electrical controls to effect the reduction in the night temperature, additional wiring may also be required. One system utilizing a manually wound clock to effect a reduction in night temperature is disclosed in U.S. Pat. No. 2,054,041. The clock in this patent is associated with a heater which is energized at night to heat the thermostat slightly so that it senses a temperature which is higher than the temperature of the room and is effective to maintain the room at a relatively low temperature. In order to energize the heater, additional wiring was provided in a manner which would make secondary or night control apparatus difficult to install in a building in association with an existing thermostat.
Other known air conditioning control systems for effecting a reduction in the temperature of a room during the night are illustrated in U.S. Pat. Nos. 3,599,863 and 3,620,448. The control systems illustrated in these patents utilize only two wires which are commonly run through the walls of a building between a thermostat and an air conditioning control relay or solenoid. However, the air conditioning control relay must be of a special and relatively expensive construction to enable it to be responsive to changes in characteristics of the current being transmitted to the thermostatic controls. When a control system having this construction is utilized with an existing air conditioning system, the existing relay must be removed and the special relay installed.
To some extent at least, the problems of the aforementioned prior art apparatus would be alleviated by utilizing the air conditioning control system disclosed in U.S. Pat. No. 3,891,144. This air conditioning control system utilizes a clock which is energized by electrical energy conducted through the two leads normally found in the wall of a building without the use of special control solenoids. However, the clock in this control apparatus is operated with substantially less power than is normally taken to operate a clock. Therefore, the clock must be of a special and relatively expensive construction. In addition, the control apparatus connected with the clock utilizes a complicated arrangement of mercury switches.